1. Discussion of the Prior Art
This invention relates to an apparatus for handling tubular goods such as pipe, casings, collars, etc. and more particularly to an apparatus for transferring tubular goods between a drilling rig and a pipe rack.
In the prior art there are various methods and devices for lifting tubulars to and from a drilling rig floor. One of such methods simply attaches a wire cable to the pipe and then the cable is lifted by a hydraulic winch which is typically mounted on a truck parked near the rig. Cranes have also been used to lift the pipe. Hydraulic driven chains have been successfully used too. Pipe transferred by these methods can be dropped on personnel or equipment below causing severe injury and damage inasmuch as they can weigh thousands of pounds. Often the pipe must be lifted to heights of forty feet or more. These dangers are more intense when the apparatus and rig are positioned offshore and subjected to wave, tidal and wind forces. If the pipe is dropped or banged against other structure the threaded ends can be easily damaged or the pipe bent.
Inclined troughs for the transfer of tubulars have also been used wherein the tubular is frictionally slid along the trough surface. This action often causes excessive wear on pipe especially the threaded ends which must be protected from such wear. It was thus often necessary to keep the metal thread protector on as the pipe was moved along the trough for removal when the pipe was on the drilling rig platform. This necessary care of the threads and pipe ends creates an extra step in the installation of the pipe or other tubular in the hole resulting in a longer cycle time.
Prior art troughs sometimes were designed to pivot from a generally horizontal position adjacent the pipe rack to an inclined position near the drilling rig floor. However, no satisfactory means had been developed for supporting the uppermost end on the floor. Also, the pivoted trough lifting mechanism and the structural integrity of the trough limited the length of the trough, the angle of inclination and hence the ultimate lifting height. When the prior art transferring apparatus was used on offshore rigs, the wind, tidal and wave forces would act against the pivoting trough causing it to sway or to become out of alignment with the support means.
From a single drilling rig often 20 or more holes are bored. This requires that the tubular handling apparatus be moved around on the platform to position it near the hole being used. This is a time-consuming process and typically requires the use of additional moving equipment, e.g. cranes.
To transfer the pipe from the ground onto the prior art pipe handling apparatus also required at least two personnel manually to move or roll the pipe to the machine, a procedure that limits the pipe from being efficiently stacked. Space being at a premium on any offshore rig, the inability efficiently to stack the pipe presents a serious problem. Inclined conveyor systems had been used to handle tubulars in the past but they occupied such large amounts of valuable floor space that they are not in any substantial use today.